Geographic distribution of Rickettsia parkeri in its US tick vector, Amblyomma maculatum, was evaluated by PCR. R. parkeri was detected in ticks from Florida, Georgia, Kentucky, Mississippi, Oklahoma, and South Carolina, which suggests that A. maculatum may be responsible for additional cases of R. parkeri rickettsiosis throughout much of its US range.
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The Gulf Coast tick, Amblyomma maculatum (Figure), is a Nearctic and Neotropical hard tick found in coastal areas of the southern United States, with inland range extensions in Kansas, Oklahoma, and some other states. It is also found in regions of several Central and South American countries that border the Gulf of Mexico and Caribbean Sea, including Mexico, Guatemala, Belize, Nicaragua, Honduras, Costa Rica, Colombia, Venezuela, and some parts of Ecuador and Peru (1).
Rickettsia parkeri, a member of the spotted fever group rickettsiae, was initially identified in Gulf Coast ticks in 1937 (2). In 2004, the first confirmed human infection with R. parkeri was reported (3). Since that report, confirmed cases of R. parkeri rickettsiosis have been identified in other persons in Mississippi, Virginia, and possibly other US states (4-6). Only a few studies, each conducted >50 years ago, document the occurrence of R. parkeri in A. maculatum ticks (2,7,8). No contemporary surveys have documented the range of R. parkeri in the United States or the frequency of R. parkeri infection in collections of individual Gulf Coast ticks.
The Study
A. maculatum ticks collected during 1996-2005 were evaluated by molecular methods for evidence of infection with R. parkeri. Ticks were collected from various locations in Florida, Georgia, Kentucky, Mississippi, Oklahoma, and South Carolina. Most were questing adults collected from vegetation by using flannel cloth flags; a few crawling, nonattached, nonengorged adults were obtained (4 from a coyote and 3 from human hosts), and 1 engorged nymph was removed from a cotton rat. Ticks were preserved in 70% ethanol or frozen at -80°C until evaluation.
Most individual ticks were minced with a sterile scalpel blade, and DNA was extracted by using a QIAamp Mini Kit (QIAGEN, Inc., Valencia, CA, USA). Others were minced or crushed after freezing in liquid nitrogen, and DNA was extracted by using an IsoQuick nucleic acid extraction kit (ORCA Research, Bothell, WA, USA). DNA extracts were evaluated by using nested or heminested PCR assays designed to amplify a segment of the rompA gene. For the primary stage of each assay, 5 µL of extract and primers 190-70 and 190-701 (9) were used. For the nested reaction, 2 µL of completed primary reaction was used as template with primers 190-FN1 (5'-AAG CAA TAC AAC AAG GTC-3') and 190-RN1 (5'-TGA CAG TTA TTA TAC CTC-3'); for the heminested reaction, primers 190-FN1 and 190-701 were...